Filling holes in external wall (+tiling on floorboards)

Folks,
Before I start I am NOT a DIY genius, so I will probably say a lot of stupid
things......
I am getting my bathroom changed at the minute - it's a bit of a nightmare
and so far quite a few things have gone wrong :'(... Anyhow one of the
things I now need to know is how to block up two reasonably large holes in
an external wall (maybe about 5cm diameter on inside - probably bit bigger
on outside) - these used to take waste pipes, which have now moved. I can
look through the holes - you see the internal wall, the insulation (fibre
type stuff), the external wall and then the outside world.
Basically I want to know what is the best way to block up these holes. On
the inside it just needs to be left flat enough to tile over (may be getting
a plasterer anyway so he can probably sort the flat bit out)... On the
outside the house is made of block and rendered so think that should be
easier than a nice brick house.
I have used that expanding foam stuff before, but not sure how that would
work here because of the cavity between the two walls..... also if I used
this how should I finish it off on the outside of the house?
A sneaky second question on a different topic.........
We will be having the bathroom floor tiled. There are floorboards down, and
I was told to lay plywood. The tiler said 1/4 inch plywood would do. A
joiner who was looking at the doors (unrelated I know) advised at least 3/8
inch. Unfortunately I hadn't got the plywood before my plumber started
putting stuff in and he kindly laid plywood - unfortunately it is only 1/8
inch..... I take it this useless and I would be best taking it up and
starting again with something thicker (which then means the waste pipe for
the sink will need to be changed).
OK sorry for being so thick but any sensible answers from gurus would be
welcomed.
Cheers,
Sam

I pass on question 1.
The reason for using ply before tiling on floors is
a) To provide a smooth surface
b) To add rigidity to the floor.
c) In case the subfloor doesn't like wet tile adhesive (chipboard).
Normally houses have a subfloor (like thick floorboards or chipboard) and then
the floor above it. For carpets you can just use underlay and go for it, but
tiles are fussier (being rigid) and need more support. Hence the recommendation
is to use 12mm ply fixed securely on top of the subfloor. The 3mm ply solves the
smoothing problem and possibly the moisture problem, but does very little for
the rigidity.
I used 9mm on my last bathroom (at the choice of the joiner), and this seemed
fine. If I were you I would have a look at the floor and make a call on whether
you think that there is going to be enough movement to crack the grout. If there
is, take up the ply and lay 12mm. If not, leave the 3mm and go for the tiles.
I always like to put sinks and bogs on top of the tiles in any case so it might
not be a bad thing to lift the sink etc until the tiles are in in any case.
Sam wrote:

I'd get some cement, ready mix stuff in a bucket from B&Q will do, and
fill in the holes with that. Try not to let it drop down the cavity
though in case it bridges the cavity and causes a damp problem. Little
and often is probably the best way. That will work for the outside wall
and something similar for the inside wall but maybe polyfiller or
plaster rather than cement.

: Folks,
:
: Before I start I am NOT a DIY genius, so I will probably say a lot of
stupid
: things......
:
: I am getting my bathroom changed at the minute - it's a bit of a nightmare
: and so far quite a few things have gone wrong :'(... Anyhow one of the
: things I now need to know is how to block up two reasonably large holes in
: an external wall (maybe about 5cm diameter on inside - probably bit bigger
: on outside) - these used to take waste pipes, which have now moved. I can
: look through the holes - you see the internal wall, the insulation (fibre
: type stuff), the external wall and then the outside world.
:
: Basically I want to know what is the best way to block up these holes. On
: the inside it just needs to be left flat enough to tile over (may be
getting
: a plasterer anyway so he can probably sort the flat bit out)... On the
: outside the house is made of block and rendered so think that should be
: easier than a nice brick house.
:
: I have used that expanding foam stuff before, but not sure how that would
: work here because of the cavity between the two walls..... also if I used
: this how should I finish it off on the outside of the house?
:
It's best if you can fill the holes with a block of some sort, like a bit of
the original blockwork or a bit ordinary brick, and wedge it in tight in the
holes, using a mallet or hammer and wood block, to make it rigid so they
don't fall out. Cut off any protruding bits until the face is slightly
under the level of the outside block facing. Fill any gaps with a mortar
mix, a simple two sand to one of cement mix will do, and smooth off to the
under level of the render.
Depending on what render you have, you can then mix a batch of the coloured
adhesive cement and chip, pebble dash, as required. You may even get away
with a rough sand and cement render and paint it the same colour, if the
holes are the sizes you say.
The inner wall is a case of filling the holes with an off-cut of
plasterboard, if you have or can find some, and glue them in place with
either PVA Wood Glue, the waterproof stuff is best, or a mix of plaster,
polyfilla Etc.
Try not to join anything between the outer skin and inner skin of the wall.
Any bridging of the cavity can cause dampness from the outside to get in to
the inner skin, and vice versa.
:
:
: A sneaky second question on a different topic.........
:
: We will be having the bathroom floor tiled. There are floorboards down,
and
: I was told to lay plywood. The tiler said 1/4 inch plywood would do. A
: joiner who was looking at the doors (unrelated I know) advised at least
3/8
: inch. Unfortunately I hadn't got the plywood before my plumber started
: putting stuff in and he kindly laid plywood - unfortunately it is only 1/8
: inch..... I take it this useless and I would be best taking it up and
: starting again with something thicker (which then means the waste pipe for
: the sink will need to be changed).
:
:
: OK sorry for being so thick but any sensible answers from gurus would be
: welcomed.
:
: Cheers,
: Sam
:
Tiling on floors needs a solid, unmoving base. If your floors are modern
chipboard construction, then they don't always like moisture and can belly
or may split, especially around the edges. Untreated Plywood has a good
absorbent surface for adhesives, but it is also a good idea, in fact I
believe it's a must, to give the Plywood a coating or two of diluted PVA
Glue to give your adhesives an even better grip to the surface.
Make sure the Ply is thick enough to feel rigid under bare feet. Any
movement is going to show when you lay tiles and they will start to peel off
if the floor moves. The Ply needs to be fixed at least every 10 square
inches (250 mm) with screw nails, not hammer in wire nails, as these pull
back out with the expansion and contraction of the floor. To keep the Ply
from bubbling up in different temperature conditions, you really need to use
screw nails.
Once you have fixed and primed, the PVA Glue trick, your Plywood, then you
can begin to dress your tiles. This is just a dry layout of the tiling as
it is going to be finished. This lets you see where the cuts are going to
be and if you have any tricky bits that need to be sawn around Etc.
Use a good proprietary brand of powder adhesive that is mixed with water
on-site. You'll find that ready mixed tubs will dry to quickly, even under
cold damp conditions, and crack even before you lay the first tile. I fell
for that one once, never again. Don't use a grout and adhesive mix either,
as the grout needs to be drier than the adhesive and the adhesive needs to
be wetter than the grout and the two do not go together.
So also use a grout that is mixed with water on-site, as the ready mixed
types are not worth the tub they are poured from.
Good luck with it. I hope you enjoy your first bath in your new bathroom.

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